DESCRIPTION (from author's abstract): Single unit recording techniques will be used to determine what role the substantia nigra pars reticulata (SNr) may play in the selection, planning, and initiation of saccadic eye movements. Recent experiments conducted in the superior colliculus (SC), a major recipient of nigral signals, have demonstrated the existence of independent movement preparatory and movement initiating signals in the oculomotor system. These experiments have redefined the types of information carried by a number of collicular cell types and have raised the possibility that movement preparatory signals may arise in other parts of the oculomotor system. The SNr, which participates in the generation of all types of movements, has been known for over a decade to participate in the saccadic process. Units in the SNr have been shown to reduce their level of activation immediately after visual target presentations and before saccades. However, these data cannot be directly related to any available collicular data nor can they be used to describe nigra's role in movement planning as it is understood today. These observed patterns of activation could, for example, participate in sensory processing, attentional allocation, movement specification, or movement initiation. The short-range goal of this proposal is to describe movement- related signals in the SNr with regard to the set of separable events which make up an eye movement. We plan to accomplish this by segregating nigral responses into sensory, attentional, movement specification, movement initiation, and post-saccadic eye position- related categories. The long-range goals of this project are to define the hierarchical relationships between brain regions which regulate the oculomotor system and to define the sequential processes by which eye movements, and movements in general, are produced. These insights into the control of voluntary eye movements should also provide important organizational insights into the neural control of voluntary movement in general. Specifically, the goals of this project are to determine: i) What types of saccade-related spatial information do nigral units encode? ii) What types of purely temporal saccade-related information do nigral units encode? iii) What information, if any, do nigral units encode about the position of the eye in the orbit?